The present invention relates to a control method applied to data transmission between devices connected through a network of IEEE (The Institute of Electrical and Electronics Engineers) 1394 bus lines or the like and a communication device to which the control method is applied.
AV devices transmit information to each other through a network using an IEEE 1394 serial data bus. When data transmission is performed through the bus, a synchronous communication mode is used when audio data or the like is transmitted in real time and an asynchronous communication mode is used when a static image, text data, a control command, or the like is reliably transmitted. Bands dedicated to the respective modes are used in transmission. In the IEEE 1394 scheme, the synchronous communication mode is called an isochronous communication mode, and the asynchronous communication mode is called an asynchronous communication mode.
In communication in the isochronous communication mode, a device set as an IRM (Isochronous Resource Manager) in a network manages a channel and a band. A device for executing communication in isochronous communication mode performs the process of obtaining a channel and a band for the IRM. The channel is a path for flowing isochronous data between a transmission side and a reception side. The band is in proportion to the size of a packet transmitted on one channel, and is in an amount that is inversely proportional to a transmission rate.
By using the obtained channel and band, isochronous data is transmitted between the connected devices. Devices are connected using known connection technology, including a point-to-point connection (called a PtoP connection) for connecting an output plug of one device and an input plug of another device, and a broadcast connection for performing transmission by using a channel for broadcast.
In communication in the asynchronous communication mode, an input plug and an output plug which are different from those in the isochronous communication mode are used, and communication is executed by a control process which is different from that in the isochronous communication mode.
A communication circuit included in a device connected to the IEEE 1394 bus line, as described above, has two communication modes having different communication forms. Since the communication circuit is designed such that communication in the isochronous communication mode and communication in the asynchronous communication mode can be executed, the communication circuit has the disadvantage of having a circuit configuration that has a relatively large scale and a relatively high power consumption.
In a device connected to the conventional IEEE 1394 bus line, the bus line has only two states. In one state communication through the bus line can be performed and in the other state communication through the bus line cannot be performed at all because the power supply of the device is in an OFF state or a standby state. Therefore, when the power supply of the device is turned on to set the device in a state in which communication can be performed, a communication circuit connected to the bus line is always operable to consume power for the communication process.
The communication process in the device connected to the IEEE 1394 bus line has been described above. However, a similar problem is posed in communication devices for various communication methods which can perform communication in a synchronous communication mode and in an asynchronous communication simultaneously.